Plastic closures with tamperproof bands are well known in the prior art. In general, the lower portion of the closure skirt locks around a circumferential bead or flange projecting from the outside surface of the container wall, just below the rim. The lower part of the skirt, below the protruding container bead or flange, forms a tamperproof band which must be removed before the container may be opened. Many different designs have been developed for permitting easy removal of the tamperproof band. Typically, the skirt is weakened by score lines on which the band may be torn away. Further, a tab is usually provided which the user may grasp to being pulling the tamperproof band from the remainder of the closure. To make the tab accessible, the prior art has variously employed such methods as perforating an area around the tab, thickening the skirt walls near the tab, and forming an enlarged tab extending below the bottom of the skirt.
For example, U.S. Pat. No. 3,856,171 to Rossi discloses a tab partially cut away from the skirt and connected by a plurality of frangible strips, and a thickened skirt wall near the tab. U.S. Pat. No. 3,753,511 to Ruch discloses a similar band and tab, with a weakening score line formed on the outside of the skirt. In addition, U.S. Pat. No. 4,281,774 to Mumford discloses a protruding section of skirt acting as an opening tab, resulting from a discontinuous groove on the interior side thereof.